Substrate for semiconductor light-emitting element, semiconductor light-emitting element and semiconductor light-emitting element fabrication method

ABSTRACT

A group III nitride underlayer including at least Al, having a dislocation density of ≦1×10 11 /cm 2  and a (002) plane X-ray rocking curve half-width value of ≦200 seconds is formed on a set base material. A p-type semiconductor layer group is formed above the group III nitride underlayer and includes a group III nitride in which the Ga content relative to the total group III elements is ≧50% and in which a carrier density is ≧1×10 16 /cm 3 . A light-emitting layer is formed on the p-type semiconductor layer group and includes plural mutually isolated insular crystals. An n-type semiconductor layer group is formed on the light-emitting layer and includes a Ga content relative to the total group III elements of ≧50%.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a division of U.S. application Ser. No. 10/813,565filed Mar. 30, 2004 and claims the benefit of European Application03290809.7, filed Mar. 31, 2003, the entireties of which areincorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a semiconductor light-emitting elementand a method of fabrication thereof and to a substrate for asemiconductor light-emitting element.

BACKGROUND OF THE INVENTION

Group III nitrides are used as semiconductor films by whichlight-emitting semiconductor elements are formed, and in recent yearsthere have been hopes for them as semiconductor films in semiconductorlight-emitting elements constituting, in particular, high-luminancelight sources for green light to blue light and also light sources forultraviolet light and white light.

FIG. 1 is a block diagram showing one example of a conventionalso-called PN type semiconductor light-emitting element.

In the semiconductor light-emitting element 10 shown in FIG. 1, thefollowing are successively formed on a substrate 1, which is formed, forexample, from a sapphire single crystal: a buffer layer 2 constituted byGaN, an underlayer 3 constituted by Si-doped n-GaN, an n-typeelectrically conductive layer 4 constituted by Si-doped n-AlGaN, alight-emitting layer 5, a p-type clad layer 6 constituted by Mg-dopedp-AlGaN and a p-type electrically conductive layer 7 constituted byMg-doped p-GaN.

The light-emitting layer 5 can be constituted as a single group IIInitride layer or as a multiple-quantum-well (MQW) structure, and inrecent years in particular it can also be constituted as a quantum dotstructure. This quantum dot structure presents a structure in which, as,for example, shown in FIG. 2, crystals 12-1-12-5 in the form of islandsconstituted by GaInN are formed in a base layer 17 constituted by GaN.These insular structures may be mutually isolated or they may beconnected to one another. The specific form of the insular structuresdepends on the conditions of their fabrication. In this example, theinsular structures 12-1-12-5 are so constituted that they are mutuallyisolated.

A portion of the n-type conductive layer 3 is exposed and an Al/Ti orsimilar n-type electrode 8 is formed on this exposed portion, and,further, an Au/Ni or similar p-type electrode 9 is formed on the p-typeconductive layer 7. The imposition of a set voltage across the n-typeelectrode 8 and the p-type electrode 9 results in recombination ofcarriers in the light-emitting layer 5 and emission of light of a setwavelength. This wavelength is determined by the light-emitting layer'sstructure and composition, etc.

In the semiconductor light-emitting element shown in FIG. 1, theunderlayer 3 and the n-type conductive layer 4 constitute an n-typeconductor layer group, while the p-type clad layer 6 and the p-typeelectrode 7 constitute a p-type conductor layer group.

In order to make practical use of the semiconductor light-emittingelement shown in FIG. 1, it is necessary to place the semiconductorlight-emitting element 10 in an atmosphere which does not containhydrogen, and then give the p-type conductor layer group constituted bythe p-type clad layer 6 and p-type electrode 7 an activation treatmentby effecting a heating treatment at a temperature of 400° C. or more,and lower the resistance value to a set value, eg, by separating andremoving the element hydrogen which has combined with the Mg which wasadded as a dopant (Japanese Patent No. 25407991).

However, when the light-emitting layer 5 is constituted as a quantum dotstructure such as shown in FIG. 2, the activation treatment at such ahigh temperature sometimes causes a breakdown of the quantum dotstructure. As a result, it is not possible to fabricate short-wavelengthsemiconductor light-emitting elements which can operate practicalapplications.

The object of the present invention is to provide a semiconductorlight-emitting element which can serve in practical applications, and inwhich a p-type semiconductor layer group and an n-type semiconductorlayer group are deposited on a set substrate, a quantum dot structuretype light-emitting layer is provided between the p-type semiconductorlayer group and the n-type semiconductor layer group, and the resistanceof the p-type semiconductor layer group is lowered sufficiently, and toprovide a substrate for this semiconductor light-emitting element. It isalso an object to provide a method of fabricating this semiconductorlight-emitting element.

SUMMARY OF THE INVENTION

In order to achieve the above objects, the present invention relates toa substrate for a semiconductor light-emitting element which includes,on a set base material, a group III nitride underlayer which contains atleast Al, in which the dislocation density is ≦1×10¹¹/cm² and whose(002) plane X-ray rocking curve half-width value is ≦200 seconds. Ap-type semiconductor layer group is formed on the group III nitrideunderlayer and is constituted by a group III nitride in which the Gacontent relative to the total group III elements is ≧50% and in whichthe carrier density is ≧1×10¹⁶/cm³. A light-emitting layer is formed onthe p-type semi-conductor layer, which presents the form of insularcrystals constituted by a group III nitride and which produces quantumeffects. An n-type semiconductor layer group is formed on thelight-emitting layer and in which the Ga content relative to the totalgroup III elements is ≧50%.

The invention further relates to a semiconductor light-emitting elementwhich includes a set base material having a group III nitride underlayerformed thereon, which contains at least Al, in which the dislocationdensity is ≦1×10¹¹/cm² and whose (002) plane X-ray rocking curvehalf-width value is ≦200 seconds. A p-type semiconductor layer group isformed on the group III nitride underlayer, which is constituted by agroup III nitride in which the Ga content relative to the total groupIII el ements is ≧50% and in which the carrier density is ≧1×10¹⁶/cm³. Alight-emitting layer is formed on the p-type semiconductor layer, whichpresents the form of insular crystals constituted by a group III nitrideand which produces quantum effects. An n-type semiconductor layer groupis formed on the light-emitting layer and in which the Ga contentrelative to the total group III elements is ≧50%.

Further, the invention relates to a semiconductor light-emitting elementfabrication method which includes: a step of forming, on a set basematerial, a group III nitride underlayer, which contains at least Al,has a dislocation density of ≦1×10¹¹/cm² and whose (002) plane X-rayrocking curve half-width value is ≦200 seconds; a step of forming, onthe group III nitride underlayer, a p-type semiconductor layer groupwhich is constituted by a group III nitride in which the Ga contentrelative to the total group III elements is ≧50%; a step of forming, onthe p-type semiconductor layer, a light-emitting layer which presentsthe form of insular crystals constituted by a group III nitride andwhich produces quantum effects; and a step of forming, on thelight-emitting layer, an n-type semiconductor layer group in which theGa content relative to the total group III elements is ≧50%.

The present inventors conducted intensive research in order to achievethe objects noted above. As a result of this research, a group IIInitride underlayer, such as described above, which contains Al and highcrystal quality is provided on a set substrate, and a p-typesemiconductor layer group and an n-type semiconductor layer group areconstituted by group III nitrides having Ga as a principal component.Further, it was discovered that by following the fabrication method ofthe invention, reversing the deposition order of the p-typesemiconductor layer group and n-type semiconductor layer group in aconventional semiconductor element structure, such as shown in FIG. 1,and forming the above noted p-type semiconductor layer group with acarrier density of ≦1×10¹⁶/CM³ before the light-emitting layer and theabove-noted n-type semiconductor layer group are deposited, alight-emitting layer can be constituted and the resistance ofabove-noted p-type semiconductor layer group can be reduced sufficientlywithout causing a breakdown of the quantum dot structure which producesquantum effects. Thus, according to the invention, a semiconductorlight-emitting element, which has a light-emitting layer possessing aquantum dot structure, can serve in practical applications and can beprovided by a very simple process.

According to the invention, at the time of carrier confinement, sincethe light-emitting layer presents the form of a quantum dot structure,carrier confinement can be satisfactorily achieved even without makinguse of a double heterodyne structure such as one in which a quantum wellstructure is employed. Therefore, there is no need for the provision ofa clad layer which is such as employed in a double heterodyne structure,etc. and whose bandgap is greater than that of the light-emitting layer.This is because the bandgap of the matrix material of the light-emittinglayer containing the quantum dots is greater than the bandgap of thequantum dots in the light-emitting layer, and, consequently, a doubleheterodyne structure is formed in the light-emitting layer. In thisSpecification, a double heterodyne structure such as this will be calleda pseudo-double-heterodyne structure.

Further, if the arrangement is made such that the light-emitting layeris constituted by plural layers, the result is that pluralpseudo-double-heterodyne structures are formed in the light-emittinglayer, and the carrier confinement effect is further improved.

However, the invention is not one in which clad formation is completelyexcluded. As in the past, the carrier confinement effect can be improvedby forming a clad layer adjacent to the light-emitting layer.

Formation of a p-type semiconductor layer group whose carrier density isequal to or greater than that noted above can be achieved by effectingan activation treatment in the form of a heat treatment at a hightemperature after the p-type semi-conductor layer group has been formed,or by forming the p-type semiconductor layer group by a MBE procedure. Acombination of these two procedures is of course effective.

According to the invention, sufficient activation and reduction of theresistance of the above noted p-type semiconductor layer group can beeffected and a semiconductor light-emitting element, which can serve inpractical applications, can be provided not only in the case of a heattreatment at a high temperature, such as noted above, but also in thecase in which a heat treatment is effected at quite a low temperature.

The “insular crystals” in the invention can be so formed that they aremutually independent or they can be formed in a reticulate form in whichthey are mutually connected via thin layers. The specific forms dependon the insular crystals' fabrication conditions, etc.

BRIEF DESCRIPTION OF THE DRAWINGS

For a full understanding of the nature and objects of the invention,reference should be made to the following detailed description of theinvention, read in connection with the accompanying drawings in which:

FIG. 1 is block diagram showing one example of a conventionalsemi-conductor light-emitting element;

FIG. 2 is a schematic showing the structure of a light-emitting layerwhich constitutes a semiconductor light-emitting element;

FIG. 3 is a block diagram showing one example of a semiconductorlight-emitting element of the invention; and

FIG. 4 is a schematic showing the structure of a light-emitting layerwhich constitutes a semiconductor light-emitting element.

DETAILED DESCRIPTION OF THE INVENTION

Below, a form of implementation of the invention will be described indetail.

FIG. 3 is a block diagram showing one example of the semiconductorlight-emitting element of the invention. In the semiconductorlight-emitting element 30 shown in FIG. 3, an underlayer 23, a p-typeelectrically conductive layer 24, a light-emitting layer 25, an n-typeclad layer 26 and an n-type electrically conductive layer 27 aresuccessively provided on a substrate 21. Further, a portion of thep-type conductive layer 24 is exposed, a p-type electrode 28 constitutedby, eg, Au/Ni is formed on this exposed p-type conductive layer 24, andan n-type electrode 29 constituted by, eg, Al/Ti is formed on the n-typeconductive layer 27, thereby producing a so-called PN type semiconductorlight-emitting element.

The light-emitting layer 25 presents the form of a quantum wellstructure in which, as shown in FIG. 2, plural insular crystals12-1-12-5, which are constituted by a set group III nitride, aredisposed to be mutually isolated from one another in a base layer 17,which is also constituted by a set group III nitride.

In FIG. 3, the p-type conductive layer 24 constitutes a p-typesemiconductor layer group, and the n-type clad layer 26 and the n-typeconductive layer 27 constitute an n-type semiconductor layer group. Ifso desired, it is also possible to omit the n-type clad layer 26.

According to the invention, it is necessary that the underlayer 23 beconstituted by a high crystal quality group III nitride which containsAl, in which the dislocation density is ≦1×10¹¹/cm² and whose (002)plane X-ray rocking curve half-width value is ≦200 seconds. This resultsin the p-type conductive layer 24 which is formed on the underlayer 23acquiring substantially the same excellent crystal quality as that ofthe underlayer 23.

Since the p-type conductive layer 24 has good crystal quality, in casessuch as in which it is formed by a MBE procedure, since the MBEdeposition is effected in the absence of hydrogen, high temperatureprocedures to activate the p-type dopant are not required after growthto the active region which, in turn, prevents thermal degradation on thequantum structures. Moreover, the proportion of hydrogen uptake in thelayer can be reduced so that the amount of hydrogen that combines withthe dopant in the p-type conductive layer 24 can be reduced, and theresult is therefore that the p-type conductive layer 24 has a highcarrier density such as noted below.

Apart from the use of MBE procedures, in the case of the use of a CVDprocedure, if the p-type conductive layer 24 is given an activationtreatment by effecting a heating treatment in an atmosphere which doesnot contain hydrogen, hydrogen which has bonded with the dopant in thep-type semiconductor layer 24 can be efficiently separated and removed.Consequently, the p-type conductive layer 24 comes to have a highcarrier density such as noted below. As a result, a semi-conductorlight-emitting element 30 which is employable in practical applicationsand possesses a light-emitting layer with a quantum dot structure caneasily be produced.

It is necessary that the carrier density in the p-type conductive layer24 is ≧1×10¹⁶/cm³, and it is still more preferable if the carrierdensity is ≧1×10¹⁷/cm³. With this, the voltage drop in the p-type layercan be suppressed, a voltage can be imposed on the light-emitting layer25 efficiently, and the light emission efficiency can be improved. Inparticular, these effects become very marked when the light-emittinglayer is constituted by plural layers.

The above-noted dislocation density is preferably ≦5×10¹⁰/cm², and stillmore preferably it is ≦1×10¹⁰/cm². Also, it is preferable that the abovenoted X-ray rocking curve half-width value is ≦100 seconds, and it isstill more preferable that it be ≦60 seconds.

Further, the surface roughness Ra is preferably ≦3 Å. This measurementis made in the range of a 5 μm square by means of an atomic forcemicroscope (AFM).

The greater the Al content in the group III nitride constituting theunderlayer 23, the more the dislocations originating in the substrate 21become entangled at the interface of the substrate 21 and the underlayer23, with consequent reduction of the proportion that propagates into theunderlayer 23. As a result, the dislocation density in the underlayer 23is reduced and the crystal quality of the underlayer 23 is improved. Itis therefore preferable that group III nitride constituting theunderlayer 23 contain as much Al as possible, and, specifically, it ispreferable that it contain Al in a proportion that is ≧50% relative tothe total group III elements, and still more preferably Al constitutesthe totality of the group III elements, and the underlayer 23 isconstituted by AlN.

The underlayer 23 preferably has a great film thickness, and,specifically, it is preferably formed to a thickness of ≧0.1 μm, ≧0.5 μmbeing still more preferable. There are no particular restrictionsregarding the upper limit of the thickness of the underlayer 23, andthis is suitably selected and set taking into account the occurrence ofcracks and the purpose of use, etc.

Apart from Al, the underlayer 23 can also contain other group IIIelements such as Ga and In, etc. and additional elements such as B, Si,Ge, Zn Be and Mg, etc Also, there is not a limitation to deliberatelyadded elements, but it can also contain trace elements which areinevitably taken in depending on the film formation conditions, andtrace amounts of impurities which are contained in the source materialsand the reaction tube material.

As long as it satisfies the above-noted requirements, the underlayer 23can be formed by known film forming means. It can easily be produced byusing a MOCVD procedure and setting the film formation temperature to1100° C. or more. It is noted that the film formation temperature meansthe set temperature of the substrate 21. From considerations ofsuppression of surface roughening, etc. of the underlayer 23, it ispreferable that the film formation temperature be not more than 1250° C.

It is necessary that the p-type conductive layer 24 be constituted by agroup III nitride in which the Ga content relative to the total groupIII elements is ≧50%. This makes it possible to activate the p-typeconductive layer 24 sufficiently to make its carrier density ≧1×10¹⁶/cm³and to lower its resistance. In the invention the greater the Ga contentin the group III nitride constituting the p-type conductive layer 24,the better, and, specifically, this content is preferably ≧70%, andstill more preferably Ga constitutes the totality of the group IIIelements, and the layer consists of GaN.

The p-type conductive layer 24 contains a p-type dopant such as Zn, Beor Mg, etc. Also, it can contain Al and In, etc. as well as Ga. Further,there is not a limitation to deliberately added elements but it can alsocontain trace elements which are inevitably taken in depending on thefilm formation conditions, etc. and trace amounts of impurities whichare contained in the source materials and the reaction tube material.

If the p-type layer is given an activation treatment, this is effectedafter the formation of the p-type conductive layer 24 and before theformation of the light-emitting layer 25. Specifically, after theproduction of a multilayer film structure in which, subsequent to theformation of the p-type conductive film 24, the substrate 21, underlayer23 and p-type conductive layer 24 are stacked, a heating treatment ofthis multilayer film structure is effected in an atmosphere which doesnot contain hydrogen, eg, in a vacuum, in nitrogen gas or in anatmosphere of an inert gas such as He, Ne, Ar, Kr or Xe, etc. Thetemperature at this time is set to 300-1100° C. The treatment time ismade, eg, 10 minutes-1 hour. The above noted temperature is the settemperature of the substrate 21.

Apart from the case in which the light-emitting layer 25 has insularcrystals 12-1-12-5 formed as a single stage in the base layer 17 in themanner shown, for example, in FIG. 2, insular crystals 13-1-13-5;14-1-14-5 and 15-1-15-5 may be formed in plural stages in a base layer18 in the manner shown in FIG. 4. Such insular crystals can, forexample, be produced by making the lattice constant of the group IIInitride which constitutes the insular crystals of the light-emittinglayer 25 large relative to the lattice constant of the group III nitridewhich constitutes the p-type conductive layer 24. Thus, insular crystalscan be formed on the p-type conductive layer 24 by selecting respectivegroup III nitrides in a manner such that these conditions are satisfied,applying known film formation technology to these nitrides andsuccessively forming the p-type conductive layer 24 and thelight-emitting layer 25.

The insular crystals are formed to a minute size such that quantumeffects are produced.

At the time of formation of insular crystals in the light-emittinglayer, it is desirable to effect formation by supplying In sourcematerial beforehand, and then effecting simultaneous supply of othergroup III source materials and group V source materials. This proceduremakes it possible for formation of the insular structure to be effectedwith good control to a desired size.

Localized carriers recombine in the insular crystals constituting thelight-emitting layer 25, and any desired light can be produced andemitted on the basis of this. Thus, light of any desired colour from redto blue can be caused to be produced and emitted by suitably controllingthe size of the insular crystals, and it is also possible to cause whitelight to be produced and emitted by superimposing these colours on oneanother.

The light-emitting layer 25 can be constituted by a group III nitridewhich contains at least one out of Al, Ga and In, etc. Also, there is nolimitation to deliberately added elements, but the layer can alsocontain trace elements which are inevitably taken in depending on thefilm formation conditions, etc. and trace amounts of impurities that arecontained in the source materials and the reaction tube material.

For the n-type conductive layer 27, it is necessary that the Ga contentrelative to the total group III elements is ≧50%, and preferably thiscontent is ≧70%, and still more preferably the layer consists of GaN.This makes it possible to form a good pn junction with the p-typeconductive layer 24. The n-type conductive layer 27 contains an n-typedopant such as B, Si or Ge, etc. Also, it can contain Al and In as wellas Ga. Also, there is no limitation to deliberately added elements, butthe layer can also contain trace elements which are inevitably taken independing on the film formation conditions, etc. and trace amounts ofimpurities that are contained in the source materials and the reactiontube material.

The n-type clad layer 26 can be constituted by a group III nitride whichcontains at least one out of Al, Ga and In, etc. Also, the n-type cladlayer 26 contains an n-type dopant such as B, Si or Ge, etc.

The layers from the p-type conductive layer 24 to the n-type conductivelayer 27 described above can be formed by known film formation methods,and, as noted earlier, they can be formed easily by a MOCVD procedure.They can also be formed by a LPE procedure or a MBE procedure. The useof a MBE procedure is particularly preferable, since it makes precisecontrol possible in the process of formation of a light-emitting layerwith the quantum dot structure.

The substrate 21 can be constituted by known substrate materials such asa sapphire single crystal, a ZnO single crystal, an LiAlO₂ singlecrystal, an LiGaO₂ single crystal, an MgAl₂O₄ single crystal, an MgOsingle crystal or similar oxide single crystal, an Si single crystal, anSiC single crystal or a similar group IV or group IV-IV single crystal,a GaAs single crystal, an AlN single crystal, a GaN single crystal, anAlGaN single crystal or similar group III-V single crystal, or a boridesingle crystal such as ZrB₂, etc.

EXAMPLE

In this example of implementation, the PN type semiconductorlight-emitting element 30 shown in FIG. 3 was fabricated. A two-inchdiameter, 500 μm thick C-plane sapphire single crystal was used as thesubstrate 21, and this was placed in an MOCVD unit, for which H₂, N₂,TMA (trimethylaluminium), TMG (trimethylgallium), Cp₂Mg, NH₃ and SiH₄were laid on as a gas system. After the pressure had been set to 100torr, the temperature of the substrate 21 was raised to 1100° C. whileH₂ was flowed at an average flow rate of 1 m/sec.

After that, set quantities of TMA and NH₃ were supplied, and an AINlayer was grown to a thickness of 1 μm as the underlayer 23. In thisprocess, the TMA and NH₃ feed rates were so set that the film formationrate was 0.3 μm/hr. When examined by means of a TEM, the dislocationdensity in this AlN film was found to be 1×10¹⁰/cm². When the AlN's(002)plane X-ray rocking curve was measured, its half-width value was foundto be 60 seconds, and it was confirmed that the material had goodcrystal quality, the surface roughness (Ra) being ≦1.5 Å.

Next, the substrate temperature was set to 1080° C., and then TMG, NH₃and Cp₂Mg were flowed at a total gas average flow rate of 1 m/sec, and ap-GaN layer doped with Mg was grown to a thickness of 3 μm as the p-typeconductive layer 24. The source material feed rates were made such thatthe film formation rate was 3 μm/hr. The supply of Cp₂Mg was made suchthat the carrier density became 1.0×10¹⁸/cm³.

Next, N₂ gas was introduced into the MOCVD unit to make the interior ofthe unit a nitrogen atmosphere. Next, an activation treatment of theabove noted p-GaN layer was effected by making the substrate temperature750° C. and holding for 1 hour. The carrier density of the p-GaN at thistime was 5×10¹⁷/cm².

Next, in order to protect the p-GaN layer that had been grown, TMG andNH₃ were flowed at an average flow rate of 10 m/sec, and a GaN film wasgrown to a thickness of 100 Å. After the growth was completed, thesubstrate to which the GaN film was attached was taken out and set in aMBE unit.

7N Ga, 7N In and 6N Al were used as solid sources for the MBE unit, andatomic nitrogen produced by a high-frequency plasma unit was used as anitrogen source. An Si solid source for producing n-type material wasprovided as a dopant source.

First, the substrate was heated to 900° C., and then the GaN film whichhad become a protective layer was removed by flowing H₂. After that,insular crystals for constituting the light-emitting layer 25 were grownfrom In_(0.25)Ga_(0.75)N at 600° C. to a thickness of 20 Å and anaverage diameter of 200 Å on the p-GaN layer constituting the p-typeconductive layer 24. After that, taking the light-emitting layer 24 as abase layer, a GaN layer was grown to a thickness of 50 Å at 600° C. inorder to bury the isolated insular crystals.

Next, an Si-doped n-Al_(0.05)Ga_(0.95)N layer was grown at 600° C. to athickness of 50 Å as the n-type clad layer 26 on the above noted GaNlayer, and finally an Si-doped n-GaN layer was grown at 600° C. to athickness of 2000 Å as the n-type conductive layer 27.

Next, a portion of the p-GaN layer constituting the p-type conductivelayer 24 was exposed by effecting partial etching removal of the variouslayers, and a p-type electrode 28 constituted by Au/Ni was formed onthis exposed portion. Also, an n-type electrode 29 constituted by Al/Tiwas formed on the n-type GaN layer constituting the n-type conductivelayer 27.

It was confirmed that blue light was emitted with an emission efficiencyof 30 (lm/W) when drive was effected by imposing a voltage across theAu/Ni electrode and the Al/Ti electrode.

Comparative Example 1

A semiconductor light-emitting element was fabricated by procedure thatwas the same as in the example of implementation except that, instead ofan AlN underlayer being formed, a GaN underlayer was formed to athickness of 0.03 μm at a low temperature of 600° C. In this case,current did not flow in the semiconductor light-emitting element, andlight was not emitted.

Comparative Example 2

In this comparative example, the PN type semiconductor light-emittingelement shown in FIG. 1 was fabricated.

A sapphire single crystal was used as the substrate 1, and was placed inan MOCVD unit like that of the example of implementation. After thesubstrate 1 had been heated to 400° C., TMG and NH₃ were supplied and aGaN layer was formed to a thickness of 0.03 μm as the buffer layer 2.

After that, the supply of TMG and NH₃ was temporarily halted, thesubstrate temperature was made 1120° C., TMG, NH₃ and SiH₄ weresupplied, and an n-GaN layer 2 was formed at a film formation rate of 3μm/hr to a thickness of 3 μm as the underlayer 3. Next, formation of thelayers from the n-type conductive layer 4 to the p-type conductive layer7 was effected in the same way as in the example of implementation.After that the semiconductor light-emitting element which had beenproduced was placed in a nitrogen atmosphere which did not containhydrogen, and activation treatment was effected by heating to 750° C.and holding for 1 hour.

Then, the Al/Ti n-type electrode 8 and the Au/Ni p-type electrode 9 wereformed, and it was ascertained that blue light was emitted with anemission efficiency of 10 (lm/W) when drive was effected by imposing avoltage across the Au/Ni electrode and Al/Ti electrode.

It is seen from the example of implementation and Comparative Example 1that with a semiconductor light-emitting element possessingsubstrate/p-type semi-conductor layer group/light-emitting layer/n-typesemiconductor layer group structure produced in accordance with theinvention by forming a high crystal quality AlN underfilm and formingp-GaN, n-AlGaN and n-GaN on this AlN underfilm, the resistance of theoverall element is made lower and the light emission efficiency is madebetter than in the case of the semiconductor light-emitting element inwhich a low crystal quality GaN underfilm is formed and the structuredescribed above is formed on this GaN underfilm.

Further, it is seen from the example of implementation and ComparativeExample 2 that in the case in which, in accordance with the invention, ap-type semi-conductor layer group is formed below a light-emitting layerand an n-type semi-conductor layer group is formed above so as to give asubstrate/p-type semiconductor layer group/light-emitting layer/n-typesemiconductor layer group structure it is possible to activate only thep-type semiconductor layer group before the light-emitting layer isformed, whereas in the case in which an n-type semiconductor layer groupis formed below a light-emitting layer and a p-type semiconductor layergroup is formed above the light-emitting layer so as to give asubstrate/n-type semiconductor layer group/light-emitting layer/p-typesemiconductor layer group structure, the result is that the activationtreatment is effected with the structure from the n-type semi-conductorlayer group to the p-type semiconductor layer group made integral. Itwas found that, consequently, breakdown of the quantum dot structureconstituting the light-emitting layer was caused, and there was failureto achieve a satisfactory light emission efficiency.

Although, a specific example was taken and a detailed description of thepresent invention was given above with reference to a form ofimplementation of the invention, the invention is not limited to thecontent described above, but all sorts of variations and modificationsare possible as long as there is no departure from scope of theinvention.

For example, the substrate can be given a nitriding treatment, andpretreatment, etc. of the substrate with group III raw material can beeffected. Further, it is possible to make the composition of theunderlayer continuously varying, or to effect variation thereof withstepwise divisions made in the film formation conditions. Also, for thepurpose of improving the crystallinity of a conductive layer and alight-emitting layer, etc. still more, a buffer layer or a multilayerstructure such as a strain superlattice, etc. can be interposed betweenthe underlayer and the conductive layer, etc. by varying growthconditions such as the temperature, flow rate, pressure, source materialfeed rates and added gases, etc.

Further, although the p-type semiconductor layer group was constitutedsolely by p-type conductive layers in the semiconductor light-emittingelement described above, it is also possible to provide a p-type cladlayer above these p-type conductive layers and constitute the p-typesemiconductor layer group by the p-type conductive layers and the p-typeclad layer.

Also, in the activation treatment of the p-type semiconductor layergroup, this activation treatment can be accelerated by making theatmosphere in which the activation treatment is to be effected a plasma,or by imposing a high frequency on this atmosphere.

As described above, the invention makes it possible to provide asemi-conductor light-emitting element which can serve in practicalapplications, and in which a p-type semiconductor layer group and ann-type semiconductor layer group are deposited on a set substrate, aquantum dot structure type light-emitting layer is provided between thep-type semiconductor layer group and the n-type semiconductor layergroup, and the p-type semiconductor layer group is made low-resistanceby being sufficiently activation-treated, and to provide a substrate forthis semiconductor light-emitting element. It is also made possible toprovide a method of fabricating this semiconductor light-emittingelement.

While the present invention has been particularly shown and describedwith reference to the preferred mode as illustrated in the drawings, itwill be understood by one skilled in the art that various changes indetail may be effected therein without departing from the spirit andscope of the invention as defined by the claims.

1. A semiconductor light-emitting element fabrication method comprisesthe steps of: forming a group III nitride underlayer on a set basematerial, said group III nitride underlayer contains at least Al, has adislocation density of ≦1×10¹¹/cm² and a (002) plane X-ray rocking curvehalf-width value of ≦200 seconds; forming a p-type semiconductor layergroup above said group III nitride underlayer, said p-type semiconductorlayer group comprising a group III nitride having a Ga content relativeto the total group III elements present in the p-type semiconductorlayer group of ≧50%; forming a light-emitting layer on said p-typesemiconductor layer group, said light-emitting layer having the form ofinsular crystals comprising a group III nitride and produces quantumeffects; and forming an n-type semiconductor layer group on saidlight-emitting layer, said n-type semiconductor layer group including aGa content relative to the total group III elements present in then-type semiconductor layer group of ≧50%.
 2. The semiconductorlight-emitting element fabrication method as claimed in claim 1, whereinsaid group III nitride underlayer is formed by a MOCVD procedure at atemperature of ≧1100° C.
 3. The semiconductor light-emitting elementfabrication method as claimed in claim 1, wherein said light-emittinglayer is formed by supplying an In source material beforehand, and theneffecting simultaneous supply of other group III source materials andgroup V source materials.
 4. The semiconductor light-emitting elementfabrication method as claimed in claim 1, wherein said light-emittinglayer having said insular crystals and said n-type semiconductor layergroup are formed by means of a MBE procedure.